FOREWORD. The electrowelding department of the Pittini Group, where electrowelded lattice girders are produced

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2 FOREWORD Founded in the early Sixties, the Pittini Group began its activity, on an industrial scale, in the steel sector with a production that was absolutely new for the times: steel electrowelding, to supply the building industry with preassembled reinforcements. Since then, step by step, the whole world of construction has adopted the use of electrowelded reinforcement, such as flat or bent wire mesh and electrowelded lattice girders. The latter products in particular, Pittini electrowelded lattice girders produced in a wide range of types and designed for the most varied uses have brought about such a radical innovation in the floor slab construction techniques that today no other technology of the kind is used in Europe. Since nothing happens by chance it is evident that, if thousands of builders use electrowelded lattice girders, it is because they guarantee effective results in building industrialization. This results from the flexibility of use, from the static safety (also in seismic zones), from the easy handling and positioning, and from the building speed as well as from the economic and rational working procedures on the building site. Electrowelded lattice girders, therefore, not only became by far the most suitable reinforcement for lattice girder planks or lattice girder plates, and for floors consisting of single large surface plates (one-room plates) but find generally favourable applications in industrial floors and bridge decks as well as in building systems employing load bearing Double plate panels. This publication is intended to be a synthetic guide to the most widespread uses of lattice girders, thus maintaining a constant commitment in the research in the fields of technological processes and of finished products, aimed at developing a really industrialized construction industry, that has always been peculiar to the Pittini Ferriere Nord since their beginnings. The electrowelding department of the Pittini Group, where electrowelded lattice girders are produced 1

3 1. LATTICE GIRDER PLANK FLOORS Lattice girder plank floors find their best application in residential buildings, where they can be used both in intermediate and roof floors. Their particular characteristics allow to obtain the same if not higher structural performance and reliability as traditional floors entirely cast in place. It should be pointed out that lattice girder planks feature a good flexural rigidity even before the concrete is cast; that the main bottom reinforcement is perfectly positioned and that any additional reinforcement can be positioned correctly with a much greater accuracy than in floors completely cast on site; that the diagonal wires (stirrups) create an efficient continuous connection offering great advantages with regard to shear stresses. The presence of the double stirrups, which have a 20 cm spacing, has a very positive effect: it guarantees an efficient connection between the prefabricated elements and the in situ concrete, absorbing any shear stresses. Stirrups, therefore, connect concrete and reinforcement in a very effective way. It should also be remarked that planks, owing to their low weight and their easy handling, can be efficiently used also in medium and small size building sites, with clear advantages in terms of rational results and quick erection times. Pittini lattice girders are made with steel complying with European standards pren Therefore, they constitute a high quality reinforcement that can satisfy any requirement of lightweight prefabrication. A case in which lattice girder planks are used 2

4 Lattice girder planks are made of simple and inexpensive materials, that can be easily found on the market and transported. They are: - Pittini electrowelded lattice girders; - steel bars for reinforced concrete structures; - concrete. concrete bar 4 cm cm LATTICE GIRDER PLANK Figure 1.1: components of a plank fitted with a concrete sole TOP Pittini lattice girder concrete bar 4 cm cm LATTICE GIRDER PLANK Figure 1.2: components of a plank utilizing concrete cast into a clay mould TOP Pittini lattice girder clay mould Where available, the bottom concrete of the planks can be cast into clay moulds. This last solution provides the lower surface of the floor with a homogeneous composition (a continuous clay surface); moreover, it allows to produce planks on an industrial scale. Planks can be produced either by means of automatic prefabrication systems or by artisan methods and even in the actual construction site on a concrete plane (see technical sheet on planks production, page 10). Transport, like all on site assembling operations, is very easy, due to the low weight of all the components (they usually have a weight which is lower than 12 kg for every linear meter) and to their flexural rigidity, which is very high. Lattice girder planks are therefore composed of electrowelded steel lattice girders, completed with a concrete base, that can be contained in a proper clay mould. Additional reinforcement consisting of steel bars can be positioned in the thickness of the baseboard; this is calculated according to the specific application. 3

5 A phase of the assembling operations of lattice girder planks, that can also be manually executed Lattice girder floors are easily assembled; planks are positioned at the design center to center spacing (50 60 cm) and supported by temporary props, placed at a distance of cm. They are completed with the positioning of hollow concrete or clay blocks. TOP Pittini lattice girder Reinforcing bars Figure 1.3: Layout of lattice girder and reinforcing bars in the plank Lattice girder planks require temporary props every cm 4

6 50 60 cm Figure 1.4: Lattice girder plank floors with lightweight concrete and clay blocks cm Blocks drawn in figure 1.4 enable the construction of a lightweight floor, with T- shaped load resisting elements, as can be seen in figure 1.5. If, on the other hand, specially shaped concrete elements are placed near the planks, cm H Figure 1.5: Load resisting element in a lattice girder plank floor Typical examples of plank floors: with concrete base (above) and with concrete base into a clay mould (below) 5

7 The perfectly homogeneous lower surface of a plank floor, in which the concrete of the planks is cast into clay moulds cm Figure 1.6: Section of a monolithic lattice girder plank floor cm Figure 1.7: Section of floors with double planks; with concrete hollow blocks (top) and with clay hollow blocks (bottom) cm we obtain a monolithic reinforced concrete floor. This is statically the same as a traditional cast in situ floor, requiring the use of formworks that cover the entire surface. It is therefore clear that this solution allows to obtain a great reduction in construction times and costs. If high load or span requirements have to be satisfied, there are two possible solutions: to place two or more planks together, to increase the bearing reinforcement, or to increase the height of the blocks, by putting two elements one upon the other. Once planks and blocks are put in their proper place, additional reinforcement bars to absorb negative moments at the supports and distribution reinforcement are positioned. Subsequently, concrete can be cast and levelled. During this phase, planks can support all the loads developed during the casting operations. 6

8 Figure 1.8: Monolithic concrete floor, entirely made of lattice girder planks A phase of casting in place concrete Another advantage resulting from the use of planks consists in the possibility of building with great ease cantilever elements, such as balconies, level and/or slanted roof overhangs. Lattice girder plank floors can be profitably used also in existing buildings requiring static upgrading or restoration. In this case, the reconstruction of floors is made easier by the low weight of the roof floor lattice girder planks roof overhang balcony intermediate floor Figure 1.9: Cantilever sections using lattice girder planks 7

9 Construction details Reinforcing bars for the negative moments Distribution electrowelded wire mesh 4 cm cm Lattice girder plank cm Clay block Floor composed of single planks completed with two superimposed hollow clay blocks Lattice girder plank floor with single clay blocks: section on the support Distribution reinforcement (electrowelded wire mesh) + reinforcing bars for the negative moments Distribution electrowelded wire mesh Reinforcing bars for the negative moments Reinforcing bar positioned in the plank Lattice girder plank Reinforcing bar positioned in the plank Lattice girder plank Section of in-plane beam Section of in-height beam Beam Distribution electrowelded wire mesh Reinforcing bars for the negative moments Lintels for doors and windows Lattice girder plank To support masonry Reinforcing bar positioned in the plank Section of the support Structural ribs obtained using double planks 8

10 ~ 3 m Wall anchorage B B Pittini electrowelded wire mesh 4 Ø 16 Figure 1.10: Details of plan and section of a lattice girder plank floor that substitutes an existing wood floor Stirrups Ø 6/25 TOP Pittini lattice girders components and by the effective connections that can be easily executed with the existing load bearing structures. Fig shows the plan and section of a lattice girder plank floor with clay hollow blocks replacing a wood floor on stone masonry. Plank floor in the restoration of a masonry building: the wood floor is replaced, the walls are strengthened with electrowelded wire mesh and cement mortar 9

11 Plank production: from the simplest systems to the prefabrication plants By paying a little attention and by operating with accuracy, anybody can produce lattice girder planks. The most economical and easy way is to use a concrete plane, poured in the construction site. Wooden or square steel elements with a section of 4 x 4 cm must be put on it. These elements must be fixed to the plane with a 16 cm spacing, so as to create a suitable space for the production of the plank concrete base. After the distribution on the whole surface of an ordinary demolding oil, concrete is cast in all the spaces reserved for production; it is essential that the mix be sufficiently fluid to ensure an even distribution. In this phase it is convenient to keep clean the upper surface of the elements, and remove any residual material. Subsequently, additional reinforcement and electrowelded lattice girders are positioned. The correct positioning of the reinforcing elements in the concrete cast is obtained by employing cast stoppers, provided with appropriate grooves that guarantee an adequate concrete cover. This function can also be performed by special spacers. cast stoppers Pittini lattice girders reinforcing bars Figure 1.11: A detail of the cast stoppers that enable an easy construction of lattice girder planks with concrete base square steel elements lattice girders planks It is advisable to make sure that the concrete cast is adequately vibrated, since this increases the adherence to the reinforcement. After some days, when the concrete has matured, it is possible to strip the planks and, subsequently, to assemble them. The type of production that has been just outlined is of an artisan type, but there are industrialized systems that use appropriate steel sheet planes or automated prefabrication plants enabling the production both of concrete base planks and of planks with clay moulds. In Italy, as well as in Germany, France and other European countries, such plants 10

12 A phase of industrial production of lattice girder planks whose base is cast in a clay mould have been used by groups of small-size enterprises, that have managed this way to obtain an adequate production level with low costs, while still meeting with the requirements of all partners. The industrial production of planks with concrete base (on steel sheet moulds) 11

13 2. LATTICE GIRDER PLATE FLOORS Pittini lattice girders, combined with electrowelded wire mesh, allow another interesting application in the modem industrialized construction sector: light prefabricated elements for floors to be completed on site. The concept from which they derive is the same as the one of lattice girder planks; their width is considerably increased even twenty times owing to prefabrication by means of adequate, special moulds (see Lattice girder plate production on page 24). This makes it possible for a floor to be made using a reduced number of prefabricated elements and at the same time obtaining a finish that cannot be achieved with other systems. Prefabricated plates can be used whenever a floor is to be constructed, both in civil and industrial buildings; moreover, for special requirements such as bridge deck slabs, they can be used both in connection with composite structures (steel concrete) and with main prestressed concrete beams. Lattice girder plates used in the construction of bridge decks (above) and floors in a civil building The most important advantages offered by the use of prefabricated lattice girder plates for floors in a building system are: simple execution in the prefabrication phase, with possibility of producing plates with particular shapes, whith holes, openings or interruptions in the slab and equipped with all accessories of technological plants; fast handling and installation, thanks to the large dimensions of the single elements; easy construction of floors, since the traditional formwork carpentry operations are eliminated and substituted by simple temporary props, disposed at a distance of m; moreover, this system allows to reduce the total quantity of steel that remains to be arranged on site, and enables workers to operate under conditions of maximum safety during the execution of the final concrete cast; 12

14 Right: a view of the installation on site of a floor plate. Above: a special plate with an opening. Below: piping for the electric plant, positioned over the plates, before the final concrete cast is executed elimination or reduction of temporary props, when adopting special lattice girders with higher rigidity (Pittini Baustrada lattice girders); static flexibility; plates can be designed according to all structural needs, thanks to the great variability of all the parameters; Lattice girder plate floors usually require a small number of temporary props during casting operations 13

15 Pittini lattice girders h = Ø 8 16 h = Ø 7 8 Ø 6 10 Ø 5 Ø 5 6 Ø 6 12 Figure 2.1 Section of Pittini TOP and HD Baustrada lattice girders (dimensions are expressed in mm) Floor construction utilizing self-supporting plates, that eliminate the necessity of temporary propping drastic reduction of plate soffit finishing operations; thanks to the perfectly smooth surface created by the casting plane, these operations can be limited to the sealing of the joints between the prefabricated units and to subsequent painting, or more simply to the application of wallpaper. Plates ensure a perfect lower finish of the floors; before painting the soffit, it is sufficient to seal the joints between the prefabricated units 14

16 bar concrete TOP Pittini lattice girder LATTICE GIRDER PLATE 4 cm Figure 2.2: Components of a lattice girder plank Pittini electrowelded wire mesh cm Lattice girder plates consist of a concrete slab, with a thickness of 40 to 70 mm (weighing about 100 kg/m 2 ) stiffened for transporting, lifting and installation operations by a system of electrowelded reinforcements, which consist of an embedded electrowelded wire mesh reinforcement and one or more lattice girders, only partially embedded. Reinforcing bars can be added, according to the steel section required to absorb the positive moments. Also the longitudinal wires of the mesh and the lower wires of the lattice girders concur to the realization of this steel area. Lattice girder plate dimensions can feature the most varied dimensions to suit particular applications: cm width (the length is equal to the dimensions of the rooms present in the building plan) in ordinary applications, where their dimensions are limited by those of the prefabrication plants and of the transport vehicles; dimensions and shapes to completely cover the rooms, if the prefabricated element can be produced on site. A special plate, produced on site, covers a room completely 15

17 The floor slab is obtained by placing the prefabricated plates one beside the other and is completed by the positioning of the additional reinforcement bars (distribution and for the negative moment) and with a concrete cast, having an adequate thickness. In this case a monolithic floor slab is obtained. completing concrete cast TOP Pittini lattice girder Pittini electrowelded wire mesh Figure 2.3: Section of a monolithic floor employing lattice girder plates prefabricated plate Pittini 520 L electrowelded wire mesh For lightweight floor slabs, plates are supplied from the prefabrication plant with polystyrene void formers which are positioned between the lattice girders. Slabs can be lightened also with other elements, such as blocks using either lightweight concrete or clay. block of lightweight concrete polystyrene block completing concrete cast clay block Figure 2.4: Section of a lightweight lattice girder plate floor showing various types of blocks prefabricated plate Generally, plate floor slabs feature many advantages with respect to traditional floors cast on site. This is mainly due to the following reasons: availability of a light and flexurally rigid structure before completing the concrete cast on site; elimination of the operations connected with positive moment reinforcement (it is already accurately placed in the plate in the prefabrication plant) and easy positioning of the additional negative moment reinforcement; for two way floor slabs, a part of the positive moment reinforcement is already positioned in the plate during the prefabrication phase, while the remaining one is easily placed in the construction site; it is inserted in an orthogonal position with respect to the reinforcement in the plate, passing trough the electrowelded lattice girders and on the prefabricated plate; 16

18 TOP Pittini lattice girder completing concrete cast prefabricated plate Pittini 520 L electrowelded wire mesh bearing reinforcement Figure 2.5: Two-way monolithic floor slab with plates effective continuous connection between the prefabricated element and the concrete on site (to absorb shear stresses) guaranteed by the very close double stirrups of the electrowelded lattice girders. In the case of lightweight floors, the resisting element is composed of a series of T shaped resisting structures, both for positive and negative moments (in this case the lower slab, that is the plate, contributes to the compressive strength). As stated above, the use of prefabricated plates in the floor construction guarantees distribution electrowelded wire mesh reinforcement for negative moments connecting reinforcement lattice girder plates Figure 2.6: Load resisting elements for negative and positive moments in a lightweight floor (above). Figure 2.7: Sections of beams contained in the floor thickness, executed with the plate as formwork (above) or with a prefabricated beam reinforcement for negative moments lattice girder plate beam plate TOP Pittini lattice girder connecting reinforcement a smooth soffit finish, with a homogeneous surface; in fact, it is possible to obtain beams within the overall thickness of the finished floor. Two techniques can be used for this purpose: prefabricated beam-plates (where the traditional reinforcement is partially embedded in the concrete cast) and beams placed over the plates, with the traditional reinforcement positioned over the prefabricated elements. 17

19 Lattice girder plate floor with a beam, having the same slab thickness, made with a prefabricated plate Under certain construction site conditions (bridge or viaduct structures, that must be built without interrupting the traffic or flows underneath; considerable height of the floor; slabs on canals or culverts) it may be necessary to completely eliminate temporary propping. In these cases, in addition to the use of Baustrada HD Pittini lattice girders, it can be useful to execute the casting of the central ribs. This way it is possible to obtain a self-supporting capacity of up to 6 to 7 m and to reduce, at the same time, the strain stresses during the final concrete cast. HD Baustrada Pittini lattice girders Figure 2.8: Section of a selfsupporting plate having a width of 250 cm, whose central ribs are stiffened both by Pittini Baustrada lattice girders and by a concrete cast executed in the prefabrication phase Lattice girder plate with concrete cast ribs, selfsupporting on a 6 m span 18

20 An example of steel structure with self-supporting plate floors in a civil building (offices) Lattice girder plates are the most suitable prefabricated elements for the execution of bridge decks, when pre-stressed concrete beams or steel beams are used. This allows to obtain immediately a basic element on which it is possible to carry out under maximum security conditions all the subsequent operations, while avoiding the need for costly formwork. Considering the application to bridge decks, another advantage must also be taken into account: with an adequate interruption of the concrete casting, corresponding to the connections with the beams, they can cover the whole width of the deck, including the lateral cantilever parts. The slab casting, in these cases, can be performed either in a single or in two distinct phases: the latter solution requires a lower number of lattice girders to be positioned in the cantilever section. If the final concrete cast is performed in two phases, in the first one the inner spans and a little part of the overhangs are cast; in the second one executed after some days the remaining parts of the cantilever sections are cast, after the positioning of the prefabricated vertical elements on the edges of the slab, that constitute a finished container of the concrete cast. In such a way the execution of the deck is carried out without any difficult formwork installation and also without the expensive special equipment usually required. 2nd phase b a b 1st phase a lattice girder plate Figure 2.9: Section of a caisson steel-concrete bridge. Figure 2.10: A slab executed with self-supporting plates both in the span and in the cantilever section b-b section a-a 5 HD Baustrada Pittini lattice girders 9 HD Baustrada Pittini lattice girders Pittini 520 B wire mesh Pittini 520 B wire mesh 19

21 Particularly important from a technical point of view is the mutual cooperation that is generated once the concrete cast is fully matured between the slab (deck) and the main beams to which the slab is rigidly connected (anchored) so as to create only one resisting section. A viaduct executed with a composite steel-concrete structure. The slab is built using self-supporting lattice girder plates. The photograph above shows the bearing caisson structure carried out with Cor-Ten steel Viaduct deck on pre-stressed concrete beams, executed with self-supporting plates stiffened by Pittini Baustrada HD lattice girders 20

22 interruption of the concrete cast of plates roof overhang balcony intermediate floor Figure 2.11: Section of overhanging floor parts, for roof overhangs and balconies, constructed with lattice girder plates interruption of the concrete cast of plates Adopting the same technique in civil buildings, roof overhangs and balconies are very easy to build. A peculiar application of plates with cantilever sections consist in increasing the road width in existing masonry bridges. The tecnique is very easy: after the road surface has been removed, the new deck is executed by employing special plates (without the concrete casting in the central area, A phase of placing on site special lattice girder plates for widening the road in an existing masonry bridge 21

23 The bridge during the widening operations Below: a phase of the final concrete cast corresponding to the former road pavement) whose concrete prefabricated slab is cast only near lateral cantilevers. Also in this case, on site construction operations are reduced, both with regard to the reinforcement placement (supplied almost completely embedded in the slab) and to the elimination of temporary props and formwork. As shown by the descriptions and examples reported the laying operations of the prefabricated elements are very easy, and therefore do not require special hoisting devices or skilled workers. Finishing operations are executed with extreme ease, both with regard to the installation of additional reinforcement bars and to the execution of the concrete casting. Furthermore the class of concrete for the final concrete cast has the same characteristics as those of the structures usually installed on site. 22

24 Construction details polystyrene bloks TOP Pittini lattice girders distribution electrowelded wire mesh Pittini 520 L electrowelded wire mesh bars for positive moments Section in midspan bars for negative moments distribution electrowelded wire mesh Pittini 520 L electrowelded wire mesh Section on a support TOP Pittini lattice girders bars for negative moments distribution electrowelded wire mesh lattice girder plate plate reinforcement anchoring Section on a in-height beam bars for negative moments distribution electrowelded wire mesh TOP Pittini lattice girders lattice girder plate Section on a masonry support 23

25 Plate production: a highly tested system of lightweight prefabrication Lattice girder plate production does not feature any difficulty; for a limited quantity or special production all that is required is to have a concrete track available, on which suitably shaped moulds, made of 4 5 mm thick steel sheet, can be installed. In this mould, once the transversal cast stoppers are fixed, according to the design length of the plate, the casting and levelling of the concrete are performed, on which preassembled reinforcement elements (lattice girders, wire mesh and bars) are installed. Concrete vibration allows to obtain a higher compressive strength, a good adherence to the reinforcement elements and a better lower surface of the plates. The same prefabrication track can also be installed on site. On site production of lattice girder plates: concrete spreading, reinforcement installation and subsequent vibration In general, these phases are similar also for an industrialized plate production, that takes place in special plants such as tracks fitted with vibration and, possibly, accelerated curing systems. An industrial prefabrication building yard offers the notable advantage of rationalized production phases, which guarantee a continuous production. Moreover, rationalization allows to limit the production costs while assuring productions with a constant quality level. The best solution consists in the installation of the prefabrication plant inside a covered area, equipped with an overhead travelling crane with a capacity not lower than 5 tonnes and a concrete mixing plant. In the production plant, through appropriately arranged attachments, various tracks are assembled (width cm, length 8 m) and are placed on adequate supports so that workers can operate under optimum conditions. Such elements constitute the prefabrication tracks, i.e. the plants that allow to obtain high production yields at extremely high finishing standards. 24

26 On site prefabrication of large plates for a multistorey building for dwellings Tracks allows the production of plates having a width from 50 to 250 cm, a thickness from 4 to 7 cm and variable lengths, according to design requirements. Tracks for the production of 250 cm wide plates can be equipped with longitudinal cast stoppers that allow the simultaneous production of two 120 cm wide plates. The plate reinforcement (Pittini electrowelded lattice girders, mesh and reinforcing bars) which has been preassembled in an appropriate area, is then istalled on the track previously sprayed with a demoulding compound. The length of the plates is determined by the distance between the transversal cast stoppers. It is important that the reinforcement is kept at an adequate height from the track by means of normal spacers in compliance with the concrete cover design. An element of the track for the prefabrication of lattice girder plates with a maximum width of 250 cm, equipped also with a selfadvancing vibrating trolley. Lattice girder plate casting on a prefabrication track 25

27 Then concrete is cast and, after a first spreading and levelling, it is compacted by the vibrations of the self-advancing vibrating trolley. In the case of plates designed for the production of lightweight floors with polystyrene blocks, they must be positioned on the concrete after the vibration, thus guaranteeing an adequate bond between the concrete and the block. Installation of the lightening polystyrene elements Should an accelerated production process be desired, tracks can be provided with a plant for artificial concrete curing, consisting in a heat exchanger positioned below the track composed of a coil where diathermic oil is circulated, under pressure and appropriately reheated or in a tunnel, made with polythene sheets, placed over the tracks after vibration has taken place, in which steam is blown. Plate dismantling using a special lifting device 26

28 When concrete has reached a minimum strength of 120 kg/cm 2 the following day, under normal conditions it is possible to remove the plates from the tracks. In order to avoid any cracking of the prefabricated slab as far as possible, it is necessary to evenly distribute the vertical tension, using a lifting device connected to an adequate hoisting unit. Lattice girder plates are then transported to the storage area and then shipped to the various building yards. In these phases, the rigidity of the partially embedded lattice girder gives the plates a great ease of handling; using simple fork lift trucks it is possible to perform transport and loading operations of 7-8 elements at a time. In the construction yard handling is performed by lifting the plates one by one from the truck, and positioning them directly on the area to be covered. If in the building yard there is not a crane with a 1 ton lifting capacity the operation can be performed by the truck mounted hoist. Transport of lattice girder plates Lattice girder plates being unloaded from the truck and positioned on the span to be covered by the truck hoist 27

29 3. DOUBLE PLATE PANELS The idea of employing prefabricated plates, not only for floors but also for the construction of walls, allowed the development of a new building system with partially prefabricated wall elements. At first, the system was built with two series of floor plates installed in a vertical position, mutually positioned and connected on site. Afterwards the system was made of two-plate modular elements the so called Double plate panel connected in parallel already in the prefabrication cycle by a system of special electrowelded lattice girders: the Double Plate HD Pittini. The Double-plate building system is therefore based on a prefabricated panel, Right: an apartment building, produced with the Double-plate building system. Above: a prefabricated Double-plate panel during the assembling operations composed of parallel plates that once installed on site, one beside the other and completed by an adequate connecting reinforcement and a concrete cast make up a load bearing wall. The height of this wall is equal to the height between floors, and both surfaces are perfectly finished. The Double-plate building system can be employed in all constructions, both for civil and industrial use, allowing to obtain advantages that are very similar to the ones obtained using lattice girder plates for floor slabs. The main advantages are: simple execution in the prefabrication yard, thanks to the use of the same plants as those used for lattice girder plates (see the technical sheet Production of Double-plate panel ); maximum geometric flexibility (thickness width height); possibility of executing plates with particular shapes, or fitted with openings for 28

30 Right: special Doubleplate panels for bearing walls with openings. Above: special panel equipped with fittings for the electrical system Panel installation by the use of adjustable props fixed both on the support and on prefabricated element (equipped with an anchorage system) 29

31 doors, windows or connections between orthogonal walls, to be carried out on site. The two plates can also have different dimensions: this solution is adopted for the construction of corner joints and for the connection between wall and floor; possibility of containing parts of the technological plants (electrical pipes, boxes and connections), that are inserted during the prefabrication phase; quick installation on site, thanks to the low weight (200 kg/m 2 ), to the modular dimensions of the single elements and to the simple propping operations required to main- The insertion of connecting bars between two adjacent panels or reinforcing bars at the end of the walls is simply performed tain a correct alignment and the necessary stability before the final concrete cast; simple construction of walls, since the carpentry operations required for the traditional formwork are completely eliminated by the simple use of the temporary props; reduction of the total quantity of steel bars to be positioned in the construction site, since it is strictly reduced to the ones that connect the various prefabricated panels; possibility of obtaining insulated walls, by inserting a layer of thermal insulating material in the panels during the prefabrication phases; structural flexibility: double plate panels can, in fact, satisfy all the design requirements, thanks to the great variability of all static parameters (total thickness of the final wall; quantity and quality of the reinforcing units; quality of concrete); 30

32 Right: a view of the stone slabs installation for a special finishing of the outer surface of a double-plate panel. Above: detail of the finished double plate panel. drastic reduction of the finishing operations of the outer surfaces: thanks to the perfectly smooth surface created by the casting planes, plaster can be completely eliminated, and the finishing operations can be limited to the sealing of the joints between panels and to the subsequent painting; possibility of finishing the external plate with mosaics of stone slabs or with other materials, that are put in place during the prefabrication phase. Double plate panels consist of two parallel concrete plates, with a thickness of 4 6 cm (and a weight of about 200 kg/m 2 ); they are stiffened by a system of electrowelded reinforcement, which consists of two sheets of electrowelded wire mesh (usually Ø 5 mm and 10 x 10 cm spacing) and special Double Plate Pittini lattice girders. These are inserted approximately every 50 cm, in a vertical position and create a safe connection with the wire mesh panels. Double plate panels can feature different shapes; the overall dimensions, as determined by the production plant, are: width: cm height: cm (usually it is equal to the storey height) total thickness: cm thickness of the single plate: 4 7 cm. 31

33 The double plate building system is used for the construction of external and internal load bearing walls. In the construction site the prefabricated panels are placed side by side (they are kept aligned and in a vertical position by means of adjustable concrete Double Plate HD Pittini lattice girder DOUBLE PLATE ELEMENT Figure 3.1: Components of double plate panels. Pittini electrowelded wire mesh props); then, additional connection and structural reinforcement is positioned inside. During this phase, double plate panels are hoisted and transported using hooks that are connected to the Pittini lattice girders. In the connection areas of two adjacent walls (crossings, corners, intersections) specific double plate panels are used, that are specially shaped so as to facilitate connections and the insertion of adequate structural reinforcements (see the technical sheet Construction details ). Pittini 510 electrowelded wire mesh Double Plate HD Pittini lattice girders ~ 25 ~ 50 ~ 50 ~ 50 ~ 50 ~ 25 Figure 3.2: Transversal section of double plate panel 250 cm 32

34 The casting of concrete between the two plates is performed very easily in a single phase. From a structural point of view, monolithic vertical bearing structures are thus obtained, also thanks to the effective connection between the two prefabricated plates and the concrete cast on-site, resulting from the close arrangement of the lattice girders stirrups. As a result, the double plate building system allows to obtain, in addition to a considerable resistance to vertical loads, a natural stiffness that absorbs seismic stresses without any increase in reinforcement. From this description it is already possible to appreciate the validity of the doubleplate building system. If the system is also completed using floors made of lattice girder plates, it is easily understood that the resulting building process, not only allows a considerable reduction of the equipment required on the building site, of the execution times and the number of workers but, at the same time, allowings a remarkable quality leap, since it offers extremely advanced and wholly industrialized building solutions. As stated above, double plate panels designed for the construction of external walls can be equipped with an adequate layer of insulating material (polystyrene); in the Final concrete cast of walls built with doubleplate panels. Above: a double plate panel equipped with a layer of thermal insulating material same way, plates for external walls may contain a layer of acoustic insulation, with a thickness from 2 to 5 cm. We have already mentioned that double plate panels can be executed also with openings designed for doors and windows. They are easily executed by arranging adequate cast stoppers on the prefabrication tracks. In the construction yard, the openings for doors and windows can be finished with prefabricated outer casings or traditional wood moulds that act as cast stoppers during the execution of the final concrete cast. Double plate panels can be used also for the construction of retaining walls and for fencing. 33

35 An other interesting application of the double plate building system is the construction of artificial, covered canals with a square/rectangular cross-section. After the construction of the foundations, double plate panels are installed on site, to form the lateral walls of the canal. That will be subsequently covered by self-supporting lattice girder plates. The concrete casting of the walls and the horizontal slab that do not require form- Double plate panels with openings for doors and windows, equipped with prefabricated outer casings allowing the execution in a single cast for the whole height of the wall An earth retaining wall executed with double plate elements on whose outer surface stone elements are arranged in a mosaiclike shape. Above: a fence wall, entirely executed with double plate panels 34

36 work will result in a monolithic work, able to resist both to internal and external pressures that can be caused by undergroud laying of the whole structure and by the superimposed loads. HD Baustrada Pittini lattice girders self-supporting plates Double Plate HD Pittini lattice girders double plate element connecting reinforcement from the foundation Figure 3.3: transversal section of an artificial canal constructed with double plate panels and covered by self-supporting lattice girder plates foundation A length of an artificial covered canal, constructed with double plate elements and lattice girder plates 35

37 Construction details HD Double Plate Pittini lattice girders double plate element Pittini HD 510 electrowelded wire mesh connecting reinforcement Connection of the wall to the continuous foundation connecting reinforcement reinforcement for negative moments double plate element lattice girder plate floor Connection between floor and external wall 36

38 reinforcement for bending stresses of the two walls 50 cm 50 cm Corner connection of two walls reinforcement for bending stresses of the two walls HD Pittini lattice girders Connection of an internal and an external wall 37

39 Some constructions performed using the double plate building system 38

40 Prefabrication of double plate panels The manufacturing process of double plate panels can also be carried out using the same standard plant with fixed moulds described for the production of lattice girder plate floors. The first plate is manufactured in the same way as a floor, and then the second plate is manufactured after having extracted, tilted and positioned the first plate manually on the same mould. The mould is prepared with the concrete and the reinforcement for the second plate, so that the two plates will be constructed perfectly parallel. The new plants for the production of lattice girder plates or double plates are equipped with a carousel system. This system allows the operators to remain in a fixed position while the moulds are automatically moved from one working area to the other, following a circular path controlled by appropriate software. In these plants, many processes are automated. Operations such as cleaning the moulds, plotting, positioning the magnets and cast stoppers, casting the concrete, tilting the first plate and coupling the plates to obtain the double plate panel are all carried out automatically so as to rationalize the process and avoid human errors. Equipment for cleaning and placing the transverse cast stoppers (photo CEIS - TN) 39

41 Carousel production cycle Once the project is confirmed by the customer, all the construction details of each double plate panel are processed using specific software, so as to provide on-line all the information required by the various working stations. The process starts after delivering the manufactured articles, when the production track is taken to the cleaning area. Use of the laser equipment to place the magnets and the longitudinal cast stoppers. (photo CEIS - TN) A robotized machine eliminates the residues of concrete of the previous production and cleans the surface. In the following station, the geometries of the elements are directly drawn on the mould with a laser equipment. Then the magnets with relevant cast stoppers and any necessary window or door frames are automatically positioned together with the prop fixing bushes. A de-moulding compound is automatically spread and then reinforcement, lattice girders and lifting hooks are positioned. In another station, a concrete distributor moves over the mould in order to form an even layer of concrete having the thickness required by the project; then the concrete casting is compacted by vibration. Once the first plate has been completed, the moulds are stocked in the curing chamber using a special lifting equipment. 40

42 Tilting station for the first plate (photo CEIS - TN) Concrete casting of the second plate (photo CEIS - TN) 41

43 Right: after coupling the two plates, the unit is vibrated. Above: storage of a double plate panel (photo CEIS - TN) The concrete is cured at controlled temperature and humidity. After about six hours, when the concrete has reached a resistance of at least 150 kg/cm 2, the plate can be extracted from the curing chamber and taken to the tilting station. An automated system lifts and then rotates the mould together with the cured plate by 180 and finally places it over the previously produced plate. The coupling is completed by adding the necessary reinforcements, and then the mould with the two plates is taken to the curing chamber. After the curing of the second plate has been completed, the mould is moved with the special lifting equipment to the extraction station, where an operator removes the cast stoppers. Then the double plate panels are lifted and stacked by an overhead travelling crane equipped with special hooks. The stack is then moved with a fork lift to the storage area. 42

44 PITTINI REINFORCEMENTS: GREAT RELIABILITY ON A WORLDWIDE LEVEL The production of electrowelded reinforcements (wire fabrics, lattice girders and special reinforcements) is characterized by a continuous research on typology and, above all, by a constant process control. The final testing of the product, performed by official material testing laboratories, guarantees that the Pittini steel is suitable to be used in the most severe conditions and according to the various standards present in the world. These are the reasons why the Pittini Group represents a concrete and reliable worldwide reference point.the Group offers a wide range of steel wire fabrics and lattice girders having high quality standards. The production process is guaranteed by a quality system certified by IGQ. The customer service is completed by a wide availability of standard products with extremely quick delivery and a specialized technical and calculation Assistance Service. In the next pages the production tables are given for the Pittini reinforcements, for the realization of prefabricated plank and plate floors and of double plate panels. The IQNet and IGQ Quality System Certificates according to the International standard ISO

45 Properties of the reinforcing steel The reinforcing steels manufactured in Ferriere Nord S.p.A., company of Pittini Group, are delivered in bars, coils, welded fabric and lattice girders conforms the standard pren10080:1999. The values are given in the following table. Property Specified characteristic value Steel grade B450C B500B B500A Yield strength Re (N/mm 2 ) Ratio Rm/Re 1.15 and Elongation Agt (%) On order are available test reports in according to EN The reinforcing steels named PITTINI HD are classified B450C according to pren Above: the Pittini Group s hot rolling mill Right: Pittini Group s electrowelded mesh department 44

46 Weldable, deformed bars and coils for reinforced concreete Diameters and packaging Type Ø mm Weight (kg) Max weight (kg) Ø int. (mm) Ø ext. (mm) Height (mm) Length (m) Coil Spool Jumbo HD Pittini Bars HD Pittini Pittini lattice girders Pittini electrowelded lattice girders type TOP (stirrup spacing: 20 mm) TOP Ø of wires (mm) Lower (Øi) Upper (Øs) Stirrup (ds) Height (mm) h 5/7/5 h = 7, /7/5 h = 9, /7/5 h = 9, /7/5 h = 12, TOP Ø of wires (mm) Lower (Øi) Upper (Øs) Stirrup (ds) Height (mm) h 6/7/5 h = 12, /7/5 h = 16, /8/5 h = 20, Pittini electrowelded lattice girders type HD Baustrada (stirrup spacing: 20 mm) HD Baustrada Ø of wires (mm) Lower (Øi) Upper (Øs) Stirrup (ds) Height (mm) h 8/10/6 h = 12, /10/6 h = 16, /12/7,2 h = 16, ,2 165 HD Baustrada Ø of wires (mm) Lower (Øi) Upper (Øs) Stirrup (ds) Height (mm) h 8/12/7,2 h = 20, , /12/8 h = /16/10 h = 20, Pittini electrowelded lattice girders type HD Double Plate (stirrup spacing: 20 mm) HD Double Plate Ø of wires (mm) Lower (Øi) Upper (Øs) Stirrup (ds) Height (mm) h 6/8/6 h = 22, /8/6 h = /8/6 h = HD Double Plate Ø of wires (mm) Lower (Øi) Upper (Øs) Stirrup (ds) Height (mm) h 8/8/7 h = /8/7 h = Notes The table shows the geometrical properties of standard lattice girders type TOP, DL and Baustrada available in stock (12 m length). On order are available lattice girders with the following properties: - height from 7 to 40 cm - upper chord diameter from 7 to 16 mm - lower chord diameter from 6 to 16 mm - stirrups diameter from 5 to 10 mm - the ratio (F min / F max ) 0.60 are respected All types of lattice girders are available in length as multiple of 20 cm (min length 3.6 m). The reinforcing steels named PITTINI HD are classified B450C according to pren Øs ds Øi ht 45

47 Standard electrovelded wire fabric 200 x x 400 Type Ø wire Mesh size (mm) Sheet size (mm) Sheet surface (m 2 ) long. trans. long. trans. widht length Long. Trans. sectional sectional area area (mm 2 /m) (mm 2 /m) Sheet weight (kg) Weight/m 2 (kg/m 2 ) HD HD HD HD HD , HD HD HD HD HD HD HD HD HD HD HD Sheets/ bundle Bundle height (mm) Bundle weight (kg) Sheets/ pile Sheets/ load Weight/ load (kg) Walls Precast Type Ø wire Mesh size (mm) Sheet size (mm) Sheet Long. Transv. Sheet surface sectional area al area section- weight (m long. trans. long. trans. widht length 2 ) (mm 2 /m) (mm 2 /m) (kg) Weight/m 2 (kg/m 2 ) 520 L A B SETTO 1 S HD SETTO 1 C* HD SETTO 2 S HD SETTO 2 C* HD Sheets/ bundle Bundle height (mm) Bundle weight (kg) Sheets/ pile Sheets/ load Weight/ load (kg) * Special sheets with 70 cm overhangs in the long. wires The reinforcing steels named PITTINI HD are classified B450C in according to pren a a a a i i i i i i i Ø Longitudinal Ø Transversal Note Values reported are indicative and subject to variations depending on evolution in both the standards and production tecniques. For updated values please ask the Ferriere Nord Sales Department for technical specifications. a a a i : Longitudinal spacing a: Transversal spacing If you need detailed fabric, please define in a fully dimensioned drawing the mesh arrangement or combination of wire sizes (twin wires, special overhang, etc.). 46